Sleep Stages: NREM and REM Explained

When we sleep, the entire experience seems to flash by in an instant. From our head hitting the pillow to a rude awakening (thanks alarm), it’s almost as if it’s over before it’s even started. The reality, however, is that while we sleep, the body is busy cycling through several unique stages.

It’s during the four stages of sleep that our body processes information, repairs cells, releases essential hormones, re-energises, and more. Given just how much is going on inside our body when we sleep, we’ll break down the various phases shortly. However, first, we need to explain two overarching states: NREM and REM.

Stages of sleep

Even though there are four primary stages to sleep, every stage falls under one of the two categories below:

• (NREM): Non-rapid eye movement makes up stages 1–4. And as the name implies, there is little to no eye movement during these stages. It’s also relatively easy to wake someone while they are in NREM (specifically stage 1 and 2).

• (REM): Rapid eye movement encompasses the fourth and final sleep stage. It’s also the stage in which we experience vivid dreams. Most people also experience some kind of sleep paralysis during REM sleep, alongside changes in breathing and body temperature.

Stage 1: falling asleep

The first stage of your sleep cycle is the (hopefully) brief time between getting into bed and falling asleep. You might gently rouse or jolt as you drift off, but this is perfectly normal. Many of the changes we experience while falling asleep prepare our brain for stage 2.

Stage 2: light sleep

It’s still easy to wake during light sleep, but the second sleep stage sees some pretty significant changes to our brain waves. The result is reduced brain activity, slower heartbeat and breathing, and muscle relaxation. All of this lasts approximately 10–60 minutes.

Stage 3 & 4: slow-wave sleep

Slow-wave sleep is when our body performs essential repairs. The mind is a hive of activity, facilitating everything from muscle growth to cell repair, hormone release, and flushing toxins.

There’s also a discernible shift in brain wave patterns, with slow-wave sleep favouring delta brain waves. Stage 3 of our sleep cycle is the deepest phase, making it difficult for people to wake voluntarily. A complete slow-wave sleep cycle usually lasts 20–40 minutes.

REM sleep

As the body approaches the end of its sleep cycle, it enters the last phase—REM, or rapid eye movement. As the title implies, the body begins to stir from its slumber (eyeballs flicker, but eyelids stay shut) with increases in heartbeat and breathing. Muscles, however, enter a state of temporary paralysis.

It’s thought that during REM sleep, the focus shifts from repairing bodily functions to processing thoughts, emotions, and memories in the brain.^[1] This transition also comes with a distinct sleep phenomenon—vivid dreaming. To begin with, dreams may only last ten minutes, but each completed sleep cycle (stage 1–4) increases the total length of REM sleep.

On average, a complete sleep cycle takes roughly 90 minutes. Given that the recommendation for a healthy adult (over 18 years old) is 7–9 hours of sleep, that means you should experience at least 4–5 full sleep cycles a night.

What factors influence your sleep stages?

While it’s true that our sleep cycle naturally fluctuates from day to day, several factors can profoundly affect the quality and duration of each stage.

• Age: Babies, children, and teenagers all need more sleep than adults. The increase in brain development during adolescence means they need more downtime during sleep to carry out the processes outlined above. As such, it’s common for sleep cycles in children to be shorter (approximately 60 minutes), but they complete more per night as a result.

• Sleep pattern: Although we often try to fight it, our body loves routine—especially when it comes to sleep. Establishing a consistent sleep and wake time supports our body’s natural circadian rhythm, in turn encouraging a healthy and balanced sleep cycle.^[2] Ideally, we want to complete at least four full sleep cycles to feel rested.

• Alcohol consumption: Using alcohol to help you sleep is a double-edged sword. On the one hand, it can help us enter stages one and two more easily, but the benefit of falling asleep faster is quickly overcome by the disruption to stage 3 and REM. Notably, alcohol appears to suppress the REM stage, preventing your brain from carrying out restorative processes.^[3]

• Sleep disorders: Numerous sleep disorders increase the chance of waking at night, disrupting the flow of each sleep stage. For all the body’s ingenuity, it isn’t possible to skip sleep stages or pick up where you left off. So, every time conditions such as restless leg syndrome, sleep apnea, or insomnia wake you up, the entire sleep cycle has to restart.

• Caffeine: Great for some extra get-up and go—not so good for restful sleep. Caffeine being disruptive to sleep will likely come as no surprise, but it can also cause lasting damage to your body’s circadian rhythm. Without your internal clock to regulate functions, the body has a more challenging time initiating and completing an entire sleep cycle.

• Sleep environment: It may be tempting to let your head hit the pillow without much care for what’s going on around you, but you might be setting yourself up for failure. Light, noise, and room temperature all play a significant role in how well we sleep. It’s important to find the right balance and focus on maintaining these variables throughout the night to complete as many sleep cycles as possible.

Can you improve your sleep cycle?

We’ve listed some of the factors that can affect the stages of your sleep cycle, so it’s only right we outline potential solutions. The effectiveness of each suggestion will differ according to your lifestyle, but even small changes can significantly improve sleep quality.

• Limit blue light exposure: Avoiding bright light should be a top priority for restful sleep. Investing in blackout blinds can work wonders for sleep quality, or, for a budget-friendly option, try a sleep mask. However, a particular spectrum of light causes more disruption than others—blue light. Blue light from electronic devices plays havoc with the body’s melatonin production, which further upsets your circadian rhythm. The good news is that the effects aren’t permanent. Abstinence from your phone or other electrical devices at least an hour before bed can help your body resume balanced melatonin production.

• Control caffeine consumption: Unfortunately, many people don’t realise how long before caffeine is cleared from your bloodstream. On average, it takes up to twelve hours to fully process caffeine, so if you’re someone that likes a late-afternoon coffee, you could be creating more problems than you're solving. Either switch to decaf or limit caffeine intake after midday to reduce the impact on sleep.

• Maintain a consistent sleep schedule: For the reasons outlined earlier, sticking to the same sleep and wake times helps to maintain your circadian rhythm and all the benefits that come with it. That doesn’t mean going to sleep early or trying to force yourself to be a morning person. Instead, find a schedule that works for your lifestyle and stick to it.

• Consider supplements: Alongside several of our other tips, supplements are an excellent way to boost particular stages of the sleep cycle. For example, taking melatonin can help with falling asleep and increase overall sleep quality.^[4] Other natural options such as lavender, chamomile, and cannabinol (CBN) may support the sleep cycle in its entirety.

• Avoid alcohol: Indulging in a few drinks at the weekend isn’t going to cause significant problems to your sleep cycle. But keep the drinks flowing, night after night, and problems will occur. Remember, alcohol’s positive influence on falling asleep is not worth the disruption to later stages.

• Improve your bedroom environment: Anything you can do to create a comfortable sleeping environment will positively influence sleep. Blackout blinds to control light exposure, a fan to maintain room temperature (20°C/68°F), and earplugs for noise reduction are all viable options.^[5] Also, don’t forget to buy suitable pillows and covers. Investing in both will pay dividends for your mental and physical well-being.

With just a few small changes, you can support your body’s natural desire to complete several sleep cycles a night. The key is understanding what happens at each sleep stage, where you struggle, and which adjustments will help.

If you want to try a high-quality range of natural sleep supplements, browse the Cibdol store today. Or, to learn more about the intricacies of sleep, your circadian rhythm, and sleep hygiene, visit our CBD Encyclopedia.